linux-kernel - Re: [PATCH v2 16/23] counter: interrupt-cnt: Convert to new counter registration

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Date:   Mon, 27 Dec 2021 11:59:01 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     William Breathitt Gray <vilhelm.gray@...il.com>,
        Lars-Peter Clausen <lars@...afoo.de>, kernel@...gutronix.de,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ahmad Fatoum <a.fatoum@...gutronix.de>,
        Oleksij Rempel <linux@...pel-privat.de>
Subject: Re: [PATCH v2 16/23] counter: interrupt-cnt: Convert to new counter
 registration

On Mon, Dec 27, 2021 at 10:45:19AM +0100, Uwe Kleine-König wrote:
> This fixes device lifetime issues where it was possible to free a live
> struct device.
> 
> Fixes: a55ebd47f21f ("counter: add IRQ or GPIO based counter")
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> ---
>  drivers/counter/interrupt-cnt.c | 28 ++++++++++++++++------------
>  1 file changed, 16 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/counter/interrupt-cnt.c b/drivers/counter/interrupt-cnt.c
> index 4bf706ef46e2..9e99702470c2 100644
> --- a/drivers/counter/interrupt-cnt.c
> +++ b/drivers/counter/interrupt-cnt.c
> @@ -16,7 +16,6 @@
>  
>  struct interrupt_cnt_priv {
>  	atomic_t count;
> -	struct counter_device counter;
>  	struct gpio_desc *gpio;
>  	int irq;
>  	bool enabled;
> @@ -148,12 +147,14 @@ static const struct counter_ops interrupt_cnt_ops = {
>  static int interrupt_cnt_probe(struct platform_device *pdev)
>  {
>  	struct device *dev = &pdev->dev;
> +	struct counter_device *counter;
>  	struct interrupt_cnt_priv *priv;
>  	int ret;
>  
> -	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> -	if (!priv)
> +	counter = devm_counter_alloc(dev, sizeof(*priv));

I just picked one of these patches at random, nothing specific about
this driver...

You can not have a 'struct device' in memory allocated by devm_*()
functions for the obvious reason that now that memory is being
controlled by a reference count that is OUTSIDE of the structure itself.

So while your goal might be good here, this is not the correct solution
at all, sorry.

thanks,

greg k-h